Circulating coil cleanout tool and method

ABSTRACT

The invention relates to a tool and method for cleaning a wellbore. The tool includes a tubing string comprising an upper end and a lower end, and defining a first bore for allowing passage of fluid from the wellbore to surface; a guide string disposed inside the tubing string and defining an internal bore to run coiled tubing therethrough, the coiled tubing carrying at least one jet nozzle; at least one seal disposed around the tubing string for sealing against a well casing; at least one port defined by the tubing string and positioned above the seal for allowing fluid to pass therethrough; and at least one valve positioned below the seal to allow fluid to pass upward through the valve but not downward.

FIELD OF THE INVENTION

This invention relates to a downhole cleaning tool and method forremoving debris from a well.

BACKGROUND OF THE INVENTION

During production of oil from a well, debris such as sand, scale andparticulates may clog the perforations at the bottom of the well, andaccumulate with the production fluids within the wellbore. Such sand anddebris can halt or hinder production, and damage well equipment byabrasion. It is thus important to be able to clean and remove suchundesirable materials from the well as quickly and efficiently aspossible.

The use of coiled tubing in wellbore cleanout technology iswell-established. Conventional practices to remove debris include forexample, equipment such as concentric pipe, tubing operatedpump-to-surface bailer and coiled tubing with jetting; engineeringoperations supported with hydraulic modeling such as high-ratecirculation, forward or reverse circulation; and use of carrier fluidswith suspension capabilities.

However, such approaches are often time-consuming, labour intensive, andcostly. The required equipment is frequently mechanically complex whichelevates the possibility of mechanical failure and costs for manufactureand repair.

Despite such advances, there remains a need for an effective method forthe removal of debris from a well.

SUMMARY OF THE INVENTION

The present invention relates to a downhole cleaning tool and method forremoving debris from a well.

In one aspect, the invention provides a downhole tool for cleaning awellbore comprising:

-   -   a) a tubing string comprising an upper end and a lower end, and        defining a first bore for allowing passage of fluid from the        wellbore to surface;    -   b) a guide string disposed inside the tubing string and defining        an internal bore to run coiled tubing therethrough, the coiled        tubing carrying at least one jet nozzle;    -   c) at least one seal disposed around the tubing string for        sealing against a well casing;    -   d) at least one port defined by the tubing string and positioned        above the seal for allowing fluid to pass therethrough; and    -   e) at least one valve positioned below the seal to allow fluid        to pass upward through the valve but not downward.

In one embodiment, the seal comprises at least one ring-shaped V cuphaving an interior diameter substantially equal to the outside diameterof the tubing string, In one embodiment, the seal comprises a pair ofstacked V cups, an upper V cup being oriented upwardly and a lower V cupbeing oriented downwardly.

In one embodiment, the tubing string defines a pair of aligned, parallelspaced ports. In one embodiment, the valve comprises a ball valve. Inone embodiment, the tubing string and guide string are threadless. Inone embodiment, the guide string is sealed at its lower end. In oneembodiment, a drain or a sliding sleeve is positioned between the sealand the valve. In one embodiment, the guide string and valve areoptional components.

In another aspect, the invention provides a method of cleaning awellbore using the above tool comprising the steps of:

-   -   a) running the tool into the wellbore in proximity to        perforations;    -   b) pumping circulation fluid into an annulus defined between the        tool and well casing under sufficient pressure to force the        circulation medium upwardly through the port into the tubing        string to surface, wherein formation fluid and debris are        suctioned upwardly into the tubing string;    -   c) running coiled tubing into the guide string to position the        jet nozzle in proximity to the perforations;    -   d) pumping cleaning fluid into the coiled tubing to create a jet        stream of fluid; and    -   e) continuously pumping the circulation medium and cleaning        fluid for conveying formation fluid and debris upwardly from the        wellbore to surface.

In one embodiment, the guide string and valve are omitted from the tool.

In one embodiment, the method further comprises running a profile nippleinto the wellbore to land a blanking plug. In one embodiment, the methodfurther comprises killing the wellbore and removing the tool from thekilled wellbore. In one embodiment, kill fluid is pumped into the tubingstring to blow a drain. In one embodiment, a sliding sleeve is actuatedto allow fluid drainage.

Additional aspects and advantages of the present invention will beapparent in view of the description, which follows. It should beunderstood, however, that the detailed description and the specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described by way of an exemplary embodimentwith reference to the accompanying simplified, diagrammatic,not-to-scale drawings. In the drawings:

FIG. 1A is a diagrammatic representation of an embodiment of theinvention.

FIG. 1B is a diagrammatic representation of a transverse cross-sectionalview taken along line 1A-1A of FIG. 1A.

FIG. 2 is a diagrammatic representation of an embodiment of theinvention in an actuation position with a well.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

When describing the present invention, all terms not defined herein havetheir common art-recognized meanings. To the extent that the followingdescription is of a specific embodiment or a particular use of theinvention, it is intended to be illustrative only, and not limiting ofthe claimed invention. The following description is intended to coverall alternatives, modifications and equivalents that are included in thespirit and scope of the invention, as defined in the appended claims.

The present invention will now be described having reference to theaccompanying figures. The invention provides a downhole cleaning tooland method for removing debris from a well with minimal hydrostaticpressure being placed on the formation. The tool and method enableinjection of cleaning fluid through coiled tubing for lifting formationfluid and debris from the wellbore. A suitable fluid is also circulatedto provide enhanced lift for cleaning and removal.

A conventional gas well typically comprises a wellbore extending fromthe surface through the earth to intersect a production formation toproduce natural gas, condensate (i.e., natural gas liquids such aspropane and butane) and occasionally water. Similarly, an oil welltypically varies from a few hundred to several thousand feet in depth.The tool may be placed in vertical, horizontal or inclined wellbores.“Horizontal” means a plane that is substantially parallel to the planeof the horizon. “Vertical” means a plane that is perpendicular to thehorizontal plane. Such variations of well design are known to thoseskilled in the art.

The tool (1) is generally shown in the Figures to include a tubingstring (10), a guide string (12), a pair of seals (14 a, 14 b), at leastone port (16), and at least one valve (18). FIG. 2 shows the tool (1)mounted within the well tubular in a concentric orientation, forexample, the production casing (32) of a conventional well to contactthe wellbore fluid. As used herein, the term “concentric” refers tocomponents sharing a common center and thus a substantially uniformannular dimension. However, one skilled in the art will recognize thattwo tubular members where one has a smaller diameter and is placedwithin the other may be considered concentric, even if they do not sharethe exact geometric centre, and even if they are not circular incross-section.

The tubing string (10) comprises an upper end (20) which extends to thesurface, and a lower end (22) which extends downhole. The tubing string(10) may generally be cylindrical and defines a first bore (24) whichallows passage of circulation medium (indicated by arrow “a”) from theannulus (34); and formation fluid and debris (indicated by arrow “b”),and a mixture of cleaning fluid, formation fluid and debris (alsoindicated by arrow “b”) from the wellbore (42) to the surface.

The tool (1) provides convenient access for running coiled tubing (notshown) into the wellbore (42) by provision of the guide string (12). Theguide string (12) is generally cylindrical and defines an internal bore(26) sized to accommodate the coiled tubing which is run therethroughduring operation, The guide string (12) is disposed inside the tubingstring (10) using suitable fastening means (28) as are known in the art.

In one embodiment, the guide string (12) may be sealed at its lower end(30). The sealing of the guide string (12) prevents the entry offormation fluid and debris into the guide string (12) from the wellbore(42) when the coiled tubing is not required.

Coiled tubing is typically inserted into a completed oil wellbore forvarious operations including, but not limited to, chemical injection,servicing, and transport of bottom hole assemblies. In one embodiment, ajet nozzle (not shown) is attached to the coiled tubing in aconventional manner.

At least one seal (14 a, 14 b) is disposed around the tubing string(10), The seal (14 a, 14 b) is sized so as to seal the tubing string(10) against the well casing (32). Suitable seals (14 a, 14 b) as areknown in the art may be used. The seals (14 a, 14 b) may be formed of,for example, synthetic rubbers, thermoplastic materials,perfluoroelastomer materials, or other suitable substances known tothose skilled in the art, Appropriate seals (14 a, 14 b) aresufficiently resilient for providing a good seal and sufficiently rigidfor providing a relatively long life therefore. The dimensions of theseals (14 a, 14 b) are not essential to the invention and are dictatedby the sizes of the tubing string (10) and well casing (32).

In one embodiment, the seal comprises an upper ring-shaped V cup (14 a)and a lower ring-shaped V cup (14 b). Each V cup (14 a, 14 b) has aninterior diameter substantially equal to the outside diameter of thetubing string (10). The outer diameter of the V cup (14 a, 14 b) issubstantially equal to the diameter of the well casing (32). Each V cup(14 a, 14 b) is a resiliently flexible disk shaped body having a centralhole, The diameter of the central hole is substantially equal to theouter diameter of the tubing string (10) such that the V cup (14 a, 14b) is placed around the tubing string (10) in a collar-like manner, Thewalls of the V cup (14 a, 14 b) extend radially from the central hole atan angle below the horizontal plane of the central hole such that theouter edge of the V cup (14 a, 14 b) terminates at a position below theplane of the central hole. The upper V cup (14 a) and lower V cup (14 b)are oriented in a stacked relationship. The upper V cup (14 a) isorientated so that the cup walls extend radially upwardly towards thesurface. The lower V cup (14 b) is orientated so that the cup wallsextend radially downwardly towards the downhole.

The tool (1) includes one or more ports (16). In one embodiment, thetubing string (10) defines a pair of aligned, parallel spaced ports(16). The ports (16) are positioned above the seals (14 a, 14 b) toallow entry of the circulation medium (“a”) from the annulus (34) intothe tubing string (10). The ports (16) provide an escape route above theupper V cup (14 a) for the circulation medium (“a”) which has beeninjected into the annulus (34).

The tubing string (10) includes at least one valve (18) positioned belowthe seals (14 a, 14 b). The valve (18) is one-way, allowing fluid topass upward through the valve (18) but not downward. In one embodiment,the valve (18) comprises a ball valve. It will be understood by thoseskilled in the art that other suitable valves may be used, interchanged,or selected in accordance with the type of fluid being pumped; forexample, a ball valve may be used with lighter fluids and in the absenceof solid particulate material, while a hinged valve or a flapper valvemay be used with heavy oil or sand.

The tool (1) can be constructed from any material or combination ofmaterials having suitable properties such as, for example, mechanicalstrength, ability to withstand cold and adverse field conditions,corrosion resistance, and ease of machining.

The tool (1) may be manufactured as either an integral body or acomposite tool. In one embodiment, the tubing string (10), guide string(12), ports (16), and valve (18) are combined in an integral body. Asused herein, the term “integral” means that the body portion of thetubing string (10) is formed from a single cast or forged steel bodywhich is machined to form the guide string (12), ports (16) and valve(18). With respect to the seals (14 a, 14 b), the body portion is sizedand adapted to mount the seals (14 a, 14 b).

In one embodiment, the tubing string (10) and the guide string (12) areboth threadless. As used herein, the term “threadless” means free ofcooperating threads to interconnect components as they are aligned androtated relative to one another. The use of a threadless tubing string(10) and guide string (12) minimizes friction and restriction of fluidflow within the annulus (34) during operation. The threadlessconfiguration provides a reliable method for straight-pull emergencyshear release. A shear is effectively built into the tubing string (10)to enable positive release of the tubing string (10) in the event thatthe tool (1) becomes stuck within the wellbore (42). A relatively largework string may also be used including one or more substantially largeports (16) for circulating fluids up the tubing string (10) and allowingmore inflow with less restriction from the desired cleaning zone.

However, those skilled in the art will understand that variousmodifications can be made without altering the substance of theinvention. For example, the tool (1) may be formed from the assembly ofseparate components which may be threaded.

In one embodiment, the guide string (12) and valve (18) are optionallyomitted from the tool (1) in the event that the tubing string (10) mayhave an internal diameter which is insufficient to accommodate a guidestring (12). In this configuration, the tubing string (10) is sized toaccommodate coiled tubing which is appropriately sized to be easily runinto or removed from the tubing string (10).

Use of the tool (1) will now be described having reference to FIG. 2. Asuitable configuration for well control includes fluid injection inlets(36) having valves (38) which can be opened and closed to permit andcease the flow of fluid, and a blow-out preventer (40) which preventsthe tool (1) from being blown out of the wellbore (42) when a blowoutthreatens. Positioning of the guide string (12) inside the tubing string(10) thus allows the blow-out preventer (40) to close around both thetubing string (10) and guide string (12) to prevent them from beingblown out of the wellbore (42). In one embodiment, the blow-outpreventer (40) comprises one or more variable bore-pipe rams whichaccommodate tubulars of varying diameters and through which the tubularsare tripped. Ported crossover bodies may be used for picking up workstring.

The tool (1) is run through the blowout preventer (40) into the wellbore(42) using conventional techniques and positioned in proximity to aplurality of perforations (44) which are diametrically opposed andspaced intermittently along the casing (32) adjacent an undergroundformation (46) to enable fluid communication with the formation (46). Asused herein, the term “debris” means debris which generally exists inthe formation (46) and in the casing (32), and results from operationsincluding drilling or perforation debris, debris from cementingoperations, and from mud solids. Naturally occurring debris such assand, silts or clays may also be present in the formation (46).

The upper and lower V cups (14 a, 14 b) of the tool (1) are in a sealingengagement with the casing (32). Above the upper V cup (14 a), anannulus (34) is defined between the tool (1) and the casing (32). Thetool valve (18) is in the closed position. The casing valves (38) areopened to allow pumping of circulation medium (“a”) under pressurethrough the inlets (36) into the annulus (34). The upper V cup (14 a)acts as a physical barrier between the tool (1) and casing (32) toprevent the circulation medium (“a”) from flowing further downwardthrough the annulus (34). Upon reaching the upper V cup (14 a), thecirculation medium (“a”) is forced upwardly through the ports (16) intothe tubing string (10).

The circulation medium (“a”) which is pumped into the annulus (34) maycomprise any suitable medium including, but are not limited to, drillingfluid, water-based fluids, foaming agents, and the like. In oneembodiment, the circulation medium comprises low density foam. Foaminherently has a high viscosity at low shear rates making it extremelyuseful as a circulating medium. A variety of natural and processadditives or polymers are known in the art to increase the lifting,carrying, and suspending capability of the circulation medium.

It is to be noted that the upper V cup (14 a) prevents any hydrostaticpressure from being placed on the formation (46) since the verticalheight of the circulation medium (“a”) is minimal above the perforations(44) when pumping or at rest. As used herein, the term “hydrostaticpressure” means the total fluid pressure created by the weight of acolumn of fluid, acting on any given point in a well.

The upwards motion of the circulation medium (“a”) into the tubingstring (10) creates a Venturi effect and suctioning force which drawsformation fluids and debris (“b”) from the formation (46) through theperforations (44). The upwards motion of the formation fluid and debris(“b”) opens the tool valve (18) to pass into the tubing string (10). Thelower V cup (14 b) acts as a physical barrier to prevent the formationfluid and debris (“b”) from flowing upwards into the annulus (34), andto force the formation fluid and debris (“b”) to flow upwards throughthe tool valve (18) into the tubing string (10) to be circulated to thesurface.

Once circulation has been established, coiled tubing (not shown) is runinto the guide string (12) using conventional coiled tubing techniquesincluding, but not limited to, a kick off coil diverter. The guidestring (12) facilitates insertion of the coiled tubing and access to thewellbore (42). Further, the guide string (12) provides stability andrigidity to the coiled tubing by preventing the coiled tubing frombending or wrapping around the tubing string (10). Agitation of sandaround the coiled tubing is minimized. Further, the guide string (12)simply and effectively expedites the entry and removal of the coiledtubing from the wellbore (42) since the amount of drag is minimized.

The coiled tubing is positioned below the tool (1) in proximity to theperforations (44). Cleaning fluid is pumped under pressure through thecoiled tubing and a bottom hole assembly (not shown). In one embodiment,the bottom hole assembly comprises a jet nozzle which emits a stream ofpressurized fluid at a relatively high velocity. The pressurized fluidstream facilitates the clean out of the perforations (44), slots, andscreens, and the suspension of the formation fluid and debris (“b”)within the cleaning fluid. As the circulation of circulation medium(“a”) continues, the suspension of cleaning fluid, formation fluid, anddebris is drawn upwardly through the valve (18) into the tubing string(10). The suspension of cleaning fluid, formation fluid, and debriscombines with the circulation medium (“a”) for conveyance to thesurface. The clean out of the wellbore (42) is thus achieved bysynchronizing the pumping of cleaning fluid through the coiled tubingwith the continuous pumping of the circulation medium (“a”) into theannulus (34) to generate the desired downhole action.

The cleaning fluid (“b”) which is pumped through the coiled tubing maycomprise any suitable fluid to clean different kinds of sand and scales,and to remove wax or asphaltene build-up. Suitable fluids may include,but are not limited to, water- or oil-based fluids, water/brine,diesel/base oil, friction-reduced fluids, acids, surfactants, polymergels, foaming agents, and the like.

Upon completion of the cleaning operation, the coiled tubing iswithdrawn up through the guide string (12) for removal. A profile nipple(not shown) may be run into the wellbore (42) to land a blanking plug toprevent re-circulation of well fluids, thereby shutting in the well. Thetubing string (10) and guide string (12) can be snubbed out.

It may be desirable to circulate kill fluid into the wellbore to stopthe flow of the formation fluid. As used herein, the term “kill fluid”means any liquid pumped into a well to stop a kick (i.e., influx offormation fluid). The kill fluid is usually kill mud which is a weighteddrilling mud. In one embodiment, the tubing string (10) may include adrain (not shown) positioned between the lower V cup (14 b) and valve(18), and responsive to pressure. A kill fluid having sufficient densityto overcome production of the formation fluid is pumped into the tubingstring (10) to stop the flow and to blow the drain, resulting indraining of both the tubing string (10) and annulus (34) between thetool (1) and the casing (32) prior to tripping the tubulars out of thewellbore (42). In one embodiment, the tubing string (10) may include asliding sleeve (not shown) positioned between the lower V cup (14 b) andvalve (18). As are known in the art, sliding sleeves include ports whichcan be opened or closed by a sliding component that is generallycontrolled and operated by a slickline tool string to allow the openingor closure of flow from a zone or communication from tubing to annulus.The sliding sleeve may be actuated to allow fluid drainage from thetubing string (10) and annulus (34). It will be recognized by thoseskilled in the art that any suitable sliding sleeve as are known in theart would be appropriate for use with the present invention. Thedraining operation avoids problems commonly associated with pulling wetstrings. The tool (1) is then withdrawn up through the blowout preventer(40) for removal from the wellbore (42).

In one embodiment, the invention provides a method of cleaning awellbore using the tool comprising running the tool into the wellbore inproximity to perforations; pumping circulation fluid into an annulusdefined between the tool and well casing under sufficient pressure toforce the circulation medium upwardly through the port into the tubingstring, wherein formation fluid and debris are suctioned upwardly intothe tubing string; running coiled tubing into the guide string toposition the jet nozzle in proximity to the perforations; pumpingcleaning fluid into the coiled tubing to create a jet stream of fluid;and continuously pumping the circulation medium and cleaning fluid forconveying formation fluid and debris up the wellbore to surface.

As will be apparent to those skilled in the art, various modifications,adaptations and variations of the foregoing specific disclosure can bemade without departing from the scope of the invention claimed herein.

What is claimed is:
 1. A downhole tool for cleaning a wellborecomprising: a) a tubing string comprising an upper end and a lower end,and defining a first bore for allowing passage of fluid from thewellbore to surface; b) a guide string disposed inside the tubing stringand defining an internal bore to run coiled tubing therethrough, thecoiled tubing carrying at least one jet nozzle; c) at least one sealdisposed around the tubing string for sealing against a well casing; d)at least one port defined by the tubing string and positioned above theseal for allowing fluid to pass therethrough; and e) at least one valvepositioned below the seal to allow fluid to pass upward through thevalve but not downward.
 2. The tool of claim 1, wherein the sealcomprises at least one ring-shaped V cup having an interior diametersubstantially equal to the outside diameter of the tubing string.
 3. Thetool of claim 2, wherein the seal comprises a pair of stacked V cups, anupper V cup being oriented upwardly and a lower V cup being orienteddownwardly.
 4. The tool of claim 1, wherein the tubing string defines apair of aligned, parallel spaced ports.
 5. The tool of claim 1, whereinthe valve comprises a ball valve.
 6. The tool of claim 1, wherein thetubing string and guide string are threadless.
 7. The tool of claim 1,Wherein the guide string is sealed at its lower end.
 8. The tool ofclaim 1, comprising a drain or a sliding sleeve positioned between theseal and the valve.
 9. The tool of claim 1, wherein the guide string andvalve are optional components.
 10. A method of cleaning a wellbore usingthe tool of claim 1 comprising the steps of: a) running the tool intothe wellbore in proximity to perforations; b) pumping circulation fluidinto an annulus defined between the tool and well casing undersufficient pressure to force the circulation medium upwardly through theport into the tubing string to surface, wherein formation fluid anddebris are suctioned upwardly into the tubing string; c) running coiledtubing into the guide string to position the jet nozzle in proximity tothe perforations; d) pumping cleaning fluid into the coiled tubing tocreate a jet stream of fluid; and e) continuously pumping thecirculation medium and cleaning fluid for conveying formation fluid anddebris upwardly from the wellbore to surface.
 11. The method of claim10, wherein the guide string and valve are omitted from the tool. 12.The method of claim 10, further comprising running a profile nipple intothe wellbore to land a blanking plug.
 13. The method of claim 10,further comprising killing the wellbore and removing the tool from thekilled wellbore.
 14. The method of claim 13, wherein kill fluid ispumped into the tubing string to blow a drain.
 15. The method of claim13, wherein a sliding sleeve is actuated to allow fluid drainage.